The chief executive officer of the Irish unit of insurance giant RSA has resigned amid a probe into the firm's accounting practices.

Philip Smith said he had been made the "fall guy" in RSA's investigation into its Irish unit's capital reserves.

Smith and two other executives, chief financial officer Rory O'Connor and claims director Peter Burke, were placed on leave on November 8.

On the same day RSA injected €100m ($136 million, £83.2m) of capital into the business to keep its solvency ratio - a measure of its capacity to absorb losses - above 200%.

RSA said in a statement it estimated the "2013 operating result will be £70m lower than current market expectations. RSA Insurance Ireland has informed the Central Bank of Ireland and is working closely with them."

Smith also issued a statement: "My family and I have been truly traumatised by recent events and I have taken this most difficult of decisions in the best interests of my family.

He stated that his resignation would offer him "the opportunity to pursue justice outside the current flawed process."

After the three executives were placed on leave, RSA appointed accountancy firm PwC to look at the Irish unit's capital adequacy and the timing of reported premium payments.

PwC will report back to the board of RSA by the end of 2013.